1. Technical Field
The present invention relates to a magnetic sheet, a method of manufacturing the magnetic sheet, and an apparatus for manufacturing the magnetic sheet, and more particularly, to a magnetic sheet that may be suitable as a noise suppressing sheet, a method of manufacturing the magnetic sheet, and an apparatus for manufacturing the magnetic sheet.
2. Related Art
In general, a magnetic sheet means a sheet where a magnetic material is mixed to the inside or on the surface of a soft or hard binding sheet, and has been employed to mainly suppress radiation noise in the field of a high-frequency apparatus.
An example of a magnetic sheet in the related art is manufactured by three main steps, that is, a slurry forming step, an orientation adjusting step, a slurry sheet curing step. In the slurry forming step that is an initial step, slurry is formed by mixing a flat magnetic material in a liquid binding material. Flat soft magnetic metal powder is mainly selected as the flat magnetic material. In this step, the orientation of the flat magnetic material is not unified in one direction. Then, in the orientation adjusting step that is an intermediate step, a slurry sheet is formed by rolling the entire area of the slurry. Since the magnetic material has a flat shape, the magnetic material is transferred so as to release the pressure applied to the magnetic material mixed in the rolled slurry sheet and the in-plane direction (a direction orthogonal to the normal line of the plane) becomes parallel to the rolling direction. As a result, the orientation of the magnetic material is unified over the entire area of the slurry sheet. Further, in the slurry curing step that is a final step, the slurry sheet of which the orientation of the magnetic material is unified is cured. It may be possible to obtain a desired magnetic sheet through the above-mentioned steps (see U.S. Patent Application No. 2008003457).
In the orientation adjusting step, the orientation of the magnetic material may be unified by applying a magnetic field to the entire area of the slurry sheet in the in-plane direction of the slurry sheet after the slurry is shaped into a sheet (see Japanese Unexamined Patent Application Publication No. 2003-229694).
However, if the orientation of the magnetic material is adjusted by shaping the slurry into a sheet or applying a magnetic field to the entire area of the slurry sheet in the orientation adjusting step, the orientation of the magnetic material is unified over the entire area of the magnetic sheet. For this reason, there have been problems in that it is difficult to partially change the orientation of the magnetic material at a partial area of the magnetic sheet and the characteristics of the magnetic sheet cannot be locally changed.
For example, as described above, a magnetic sheet (a magnetic sheet where the magnetic materials are arranged laterally) where the in-plane direction of the magnetic sheet is parallel to the in-plane direction of the magnetic material has high magnetic permeability, and a magnetic sheet (a magnetic sheet where the magnetic materials are arranged longitudinally) where the normal direction of the magnetic sheet is orthogonal to the normal direction of the magnetic material has a high dielectric constant. Accordingly, the magnetic sheet where the orientation of the magnetic material is unified over the entire area of the magnetic sheet cannot but have only one characteristic of high magnetic permeability and a high dielectric constant.
In general, in order to cope with the above-mentioned problems, a double-layer magnetic sheet of which the orientation of the magnetic materials of respective layers is different has been manufactured by bonding a plurality of magnetic sheets. However, there is a concern that the double-layer magnetic sheet causes problems, such as a lack of strength of the bonded surface, a difficulty in aligning the bonding positions, and an increase in the thickness of the magnetic sheet.